The present invention relates to the field of energy beam collimators, and more particularly to an apparatus providing an array of movable blocks to define a variable aperture to allow an energy beam to be precisely controlled and directed toward the target.
In using energy beams in general, and neutron beams in particular, especially in therapeutic applications, it is necessary to be able to adjust both the size and the shape of the beam; that is to collimate the beam. At least two basic approaches to varying collimator aperture size are well known. In one technique, individual collimating devices are removed and replaced to provide variations in aperture size and shape. Generally a set of individual collimator devices having mating configurations is used. With this technique, substantial time must be spent in removing and replacing the individual collimator devices. In addition, space must be set aside for storing the individual devices when they are not in use.
A second approach to collimator aperture control is seen in U.S. Pat. No. 3,688,402 to Palermo et al in which an adjustable collimator is disclosed. The collimator is used with an X ray beam and has two web assemblies, one horizontal and one vertical. Each web assembly has a pair of spaced and connected webs forming a continuous loop over a pair of rollers. The size of the aperture is adjusted by rotating the rollers to move the interconnected web to adjust the amount of space between the ends of the webs. In this arrangement, horizontal and vertical beam opaque material overlap or are stacked in certain horizontal and vertical areas, and, as a result, twice as much beam opaque material is present in areas of overlap as compared with areas which are not overlapped. The overlapping is an undersirable and inefficient use of the beam opaque material. Thus, the basic need for a new, more efficient, approach to beam collimation is identified.
Neutrons from ion beam devices and cyclotrons are becoming increasingly important in the treatment of certain types of malignant tumors. Neutron beams, having no charge, cannot be directed and focussed by electrostatic or electromagnetic fields. To protect the patient, the beam must be attenuated and/or blocked in unwanted peripheral areas while being left an unimpeded path in a desired direction to form the desired effective beam. In other words, the beam must be collimated.
Often it is desirable to obtain a collimated beam having either diverging or converging characteristics. In U.S. Pat. No. 3,781,564 to Lundberg a neutron beam collimator providing a divergent collimated beam is disclosed. For variations in divergence characteristics, the Lundberg device requires a plurality of fixed dimension divergent beam collimators. In contrast, it would be desirable to be able to have variably adjustable divergent beam collimation.